Decacyclene as complexation manifold:: Synthesis, structure and properties of its Fe2 and Fe4 slipped triple-decker complexes

Reaction of [(eta 5-Me4EtC5)(FeCl)-Cl-II(tmeda)] (tmeda = N,N,N',N'-tetramethylethylenediamine) with a polyanion solution of decacyclene (1) results in the formation of the triple-deckers [{(eta(5)-Me4EtC5)Fe}(2)-mu(2)-(eta(6):eta(6)-decacyclene)] (3) and [{(eta(5)-Me4EtC5)Fe}(4)-mu(4)-(eta(6):eta(6):eta(6):eta(6)-decacyclene)] (4). Metal complexation in 3 and 4 occurs on opposite faces of the pi perimeter in an alternating mode. The decacyclene ring adopts a gently twisted molecular propeller geometry with twofold crystallographic symmetry (C-2). Complex 4 crystallizes in the chiral space group C222(1); the investigated crystal only contains decacyclene rings with M chirality. The handedness can be assigned unambiguously to the presence of the iron atoms. Cyclovoltammetric studies revealed quasireversible behavior of the redox events and a strong interaction of the Fe atoms in 3 and 4, exemplified by potential differences Delta E of 660 and 770(780) mV between the first and the second individual oxidation processes. This corresponds to a high degree of metal-metal interaction for 3 and 4. The sucesssful syntheses of 3 and 4 together with earlier results from our laboratory proves that all five- and six-membered pi subunit sets of I are prone to metal complexation. A clear site preference in I towards the complexation of [Cp-R]iron, -cobalt, and -nickel fragments exists.